The present invention relates to an image pickup apparatus such as a digital still camera and a video camera, and more particularly to an image pickup apparatus which has a lens barrier mechanism for protecting its lens.
Lens barrier mechanisms include a built-in lens barrier mechanism that causes plural barrier blades incorporated in a lens barrel to move between an opening position where the barrier blades are retracted so as to open a front face (hereinafter also referred to as “lens front face”) of the lens barrel and a closing position where the barrier blades are spread to cover the lens front face.
FIGS. 11, 13 and 14 show a conventional built-in lens barrier mechanism. FIG. 11 is a sectional view of a front part of a lens barrel cut by a plane passing through an optical axis of the lens barrel, which shows a state where first barrier blades 101 and second barrier blades 102 which are respectively provided in pairs are retracted to an opening position so as to overlap with each other in an optical axis direction. FIGS. 13 and 14 are front views of the lens barrel, which respectively show a state where the first and second barrier blades 101 and 102 are located at a closing position and a stare where the first and second barrier blades 101 and 102 are located at the opening position. A barrier cover 103 includes an opening portion G and a light shielding portion H, and covers an area other than an effective area of a front face of a lens 100 with the light shielding portion H.
One of the two first barrier blades 101 and one of the two second barrier blades 102 rotate around a common axis to move between the opening position and the closing position, and the other of the two first barrier blades 101 and the other of the two second barrier blades 102 rotate around a common axis to move therebetween.
Japanese Patent Laid-Open No. 2007-102086 discloses a built-in lens barrier mechanism in which three barrier blades made of metal, resin and metal are overlapped in this order to suppress increase in size of the mechanism in its optical axis direction, the increase in size being caused by increase of the number of the barrier blades.
Japanese Patent Laid-Open No. 2001-08357 discloses a built-in lens barrier mechanism that includes a pair of first barrier blades (main blades) and a pair of second barrier blades (sub blades), and each second barrier blade moves between an opening position and a closing position so as to follow movement of each first barrier blade.
Referring to FIGS. 12, 15 and 16, the built-in lens barrier mechanism disclosed in Japanese Patent Laid-Open No. 2001-083575 will be described briefly. FIG. 12 is a sectional view of a front part of a lens barrel cut by a plane passing through an optical axis of the lens barrel. The first barrier blade 111 and the second barrier blade (not shown in FIG. 12) are retracted to the opening position so as not to be overlapped with each other in an optical axis direction (that is, so as to be located on a same plane orthogonal to the optical axis). FIGS. 15 and 16 are front views of the lens barrel, which respectively show a state where the first and second barrier blades 111 and 112 are located at the closing position and a state where the first and second barrier blades 111 and 112 are located at the opening position. A barrier cover 113 includes an opening portion G and a light shielding portion H, and covers an area other than an effective area of a front face of a lens 100 with the light shielding portion H.
In the lens barrier mechanism disclosed in Japanese Patent Laid-Open No. 2001-083575, as described above, the first and second barrier blades 111 and 112 are retracted to the opening position so as not to be overlapped with each other in the optical axis direction, which makes it possible to reduce a thickness of the entire lens barrier mechanism.
In the built-in lens barrier mechanism, it is necessary to secure a space in the lens barrel into which the barrier blades are retreated from the lens front face when they are retracted to the opening position, which causes a problem of increase in outer diameter of the lens barrel.
As shown in FIG. 11, in the configuration where the plural barrier blades are overlapped in the optical axis direction to be retracted to the opening position at one side, a thickness in the optical axis direction of the entire lens barrier mechanism is increased. Thus, the opening portion of the barrier cover is located farther from the lens front face as compared with the case of FIG. 12 where the barrier blades are not overlapped in the optical axis direction. In a case where the opening portion of the barrier cover is located far from the lens front face, the opening portion has to be enlarged to prevent light rays at a same angle of view from being blocked by the barrier cover. As a result, the outer diameter of the lens barrel increases as the number of the barrier blades overlapped with each other in the optical axis direction increases.
As shown in FIG. 16, the retraction of the four barrier blades on a plane orthogonal to the optical axis at the opening position necessitates a larger area of the light shielding portion H more outside than the opening portion of the barrier cover, which results in increase of the outer diameter of the lens barrel.
As described above, in the lens barrier mechanisms disclosed in Japanese Patent Laid-Open Nos. 2007-102086 and 2001-083575, it is difficult to reduce the outer diameter of the lens barrel.